Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulosic materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulosic material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acid, e.g., acetic acid, other compounds are formed with ethanol or are formed in side reactions. These impurities limit the production and recovery of ethanol from such reaction mixtures. For example, during hydrogenation, esters are produced that together with ethanol and/or water form azeotropes, which are difficult to separate. In addition when conversion is incomplete, unreacted acid remains in the crude product, which must be removed to recover ethanol.
EP 2060555 describes a process for producing ethanol where a carbonaceous feedstock is converted to synthesis gas which is converted to ethanoic acid, which is then esterified and which is then hydrogenated to produce ethanol. U.S. Pat. No. 7,947,746 and US Pub. No. 2011/0224462 also describe a similar process where the esters produced from esterification are fed to the alcohol synthesis reactor used to produce ethanol and methanol.
WO 2009/063176 described a process for the production of ethanol from a carbonaceous feedstock, wherein the carbonaceous feedstock is first converted to synthesis gas which is then converted to ethanoic acid, which is then subject to a two stage hydrogenation process by which at least a part of the ethanoic acid is converted by a primary hydrogenation process to ethyl ethanoate, which ethyl ethanoate is converted by a secondary hydrogenation process to product ethanol.
US Pub. Nos. 2012/0010446 and 2012/0046501 describe the recovery of ethanol from a crude product obtained from the hydrogenation of acetic acid and by reacting a portion of the crude ethanol product or one or more derivative streams containing ethyl acetate obtained therefrom in the presence of hydrogen, via hydrogenolysis. The one or more derivative streams comprising ethyl acetate are reacted via hydrogenolysis to form ethanol that may be directly or indirectly fed to the separation zone or the hydrogenation reactor.
U.S. Pat. No. 6,399,812 teaches the production of aliphatic esters, R′COOR by reacting a corresponding alcohol, ROH, having carbon numbers of the alkyl groups, R′ and R, between 0 and 9 and 1 and 10, respectively, with molecular oxygen and in the presence of a dual functional catalyst comprising metal on acidic solid support. The process may be used for production of ethyl acetate by conversion of ethanol.
Therefore, a need remains for improving the recovery of ethanol from crude products obtained by reducing alkanoic acids, such as acetic acid, and other carbonyl group-containing compounds.